What can cause a mechanical multimeter's resistance range to break?
If the resistance range of the mechanical multimeter, i.e. the pointer multimeter, is damaged and other ranges can be tested normally, it indicates that the meter head should not be affected. According to the testing principle of the multimeter's resistance range, it is highly likely that the precise resistance of the shunt voltage division in the resistance range is burnt out or the resistance value changes. The most likely cause of damage to the resistance range of a mechanical multimeter is to test the voltage using the resistance range as the voltage range. So, before each test, it is important to get used to checking if the gear selection is correct and develop good testing habits.
The resistance gear of the pointer type multimeter is broken, and other gears can be used, indicating that the multimeter head is good. This is caused by incorrect use. There are two reasons for this. One is to measure the wire wound resistance of several small resistance values in the AC220V voltage burning current range when unplugged in the DC current range (regardless of the model of pointer multimeter, they are all wire wound resistors, all made of copper resistance wire, and the resistance values are very small. For example, in the MF-47 model, there are four resistors with 0.54 Ω 5.4 Ω 54 Ω 540 Ω, respectively). But the speaker said that the multimeter only has a problem with the resistance gear, so there is no problem with it occurring in this gear.
The second reason is; For beginners in electronics and electricians, after using the resistance range of a multimeter to measure components or check circuits, if the multimeter is not set to the AC 500V range and then tested for AC power in a 220V AC line or socket. There are many models and manufacturers of commonly used pointer type multimeters. The most common and commonly used ones are the old-fashioned 500 model and the MF-47 multimeter produced in Nanjing.
① The MF-47 multimeter has a DC current range (DCA), with a total of five commonly used ranges and a 5A high current expansion socket, ranging from 0~0.05mA~0.5mA~5mA-50mA~500mA.
② It has eight commonly used gears for direct current voltage (DCV) and an expansion socket that can measure DC2500V. 0~0.25V~1V~2.5V~10V~50V~250V~500V~1000V~2500V.
③ There are six levels of AC voltage (ACV), 0~10V~50V~250V~500V~2500.
④ It has five levels of DC resistance (Ω). R × 1 Ω R × 10 Ω R × 100 Ω Rx1K Ω R × 10K Ω, and a road buzzer for measurement (when the line resistance value is between 3-10 Ω, the buzzer will emit a warning sound). Due to limited space, functions such as transistor DC amplification factor hFE, infrared remote control transmission signal detection, and audio level DB are omitted.
Firstly, when measuring the resistance, the black probe is inserted into a hole → the negative pole of the meter head → a resistance of 20.2 Ω, a resistance of 220.4 Ω, and a resistance of 2430 Ω, all of which are in parallel with the meter head. At this time, the red probe is inserted into the ten sockets of the multimeter and passes through a 1A fuse tube. Then, the 1.5V dry battery is connected in series with the resistor and passed through a 20k resistor. Then, the variable potentiometer is zeroed in the 1.7k resistor range. Finally, a 500 Ω resistor is used to calibrate the R+on the other meter head. Finally, the positive pole of the meter head is marked. Once you understand the closed circuit, it's easy to handle. Based on personal experience, you can easily search for it.
Use another multimeter to look up and measure these resistances. In general, this type of fault will only burn the resistance of the resistor gear that was pulled out at the time. And these resistors are non standard values, which can be connected in series with nearby damaged resistors or replaced by a section of copper wire wrapped around a resistor. The copper wire can be cut from the wound variable potentiometer. If it is the cheaper MF-47 type with SMT, you can only ask the manufacturer for help.
If the resistance range of the mechanical multimeter, i.e. the pointer multimeter, is damaged and other ranges can be tested normally, it indicates that the meter head should not be affected. According to the testing principle of the multimeter's resistance range, it is highly likely that the precise resistance of the shunt voltage division in the resistance range is burnt out or the resistance value changes. The most likely cause of damage to the resistance range of a mechanical multimeter is to test the voltage using the resistance range as the voltage range. So, before each test, it is important to get used to checking if the gear selection is correct and develop good testing habits.
The resistance gear of the pointer type multimeter is broken, and other gears can be used, indicating that the multimeter head is good. This is caused by incorrect use. There are two reasons for this. One is to measure the wire wound resistance of several small resistance values in the AC220V voltage burning current range when unplugged in the DC current range (regardless of the model of pointer multimeter, they are all wire wound resistors, all made of copper resistance wire, and the resistance values are very small. For example, in the MF-47 model, there are four resistors with 0.54 Ω 5.4 Ω 54 Ω 540 Ω, respectively). But the speaker said that the multimeter only has a problem with the resistance gear, so there is no problem with it occurring in this gear.
The second reason is; For beginners in electronics and electricians, after using the resistance range of a multimeter to measure components or check circuits, if the multimeter is not set to the AC 500V range and then tested for AC power in a 220V AC line or socket. There are many models and manufacturers of commonly used pointer type multimeters. The most common and commonly used ones are the old-fashioned 500 model and the MF-47 multimeter produced in Nanjing.
① The MF-47 multimeter has a DC current range (DCA), with a total of five commonly used ranges and a 5A high current expansion socket, ranging from 0~0.05mA~0.5mA~5mA-50mA~500mA.
② It has eight commonly used gears for direct current voltage (DCV) and an expansion socket that can measure DC2500V. 0~0.25V~1V~2.5V~10V~50V~250V~500V~1000V~2500V.
③ There are six levels of AC voltage (ACV), 0~10V~50V~250V~500V~2500.
④ It has five levels of DC resistance (Ω). R × 1 Ω R × 10 Ω R × 100 Ω Rx1K Ω R × 10K Ω, and a road buzzer for measurement (when the line resistance value is between 3-10 Ω, the buzzer will emit a warning sound). Due to limited space, functions such as transistor DC amplification factor hFE, infrared remote control transmission signal detection, and audio level DB are omitted.
Firstly, when measuring the resistance, the black probe is inserted into a hole → the negative pole of the meter head → a resistance of 20.2 Ω, a resistance of 220.4 Ω, and a resistance of 2430 Ω, all of which are in parallel with the meter head. At this time, the red probe is inserted into the ten sockets of the multimeter and passes through a 1A fuse tube. Then, the 1.5V dry battery is connected in series with the resistor and passed through a 20k resistor. Then, the variable potentiometer is zeroed in the 1.7k resistor range. Finally, a 500 Ω resistor is used to calibrate the R+on the other meter head. Finally, the positive pole of the meter head is marked. Once you understand the closed circuit, it's easy to handle. Based on personal experience, you can easily search for it.
Use another multimeter to look up and measure these resistances. In general, this type of fault will only burn the resistance of the resistor gear that was pulled out at the time. And these resistors are non standard values, which can be connected in series with nearby damaged resistors or replaced by a section of copper wire wrapped around a resistor. The copper wire can be cut from the wound variable potentiometer. If it is the cheaper MF-47 type with SMT, you can only ask the manufacturer for help.
